Process for freeing paper pulp from impurities



May 5, 1925.

H. THOMASSEN PROCESS FOR FREEING PAPER PULP FROM IMPURITIES FIG.2.

In van for Henn ant/5 omassen.

Patented May 5, 1925.

UNITED STATES names 'rHoMA ssEN, or HEELSUM, NETHERLANDS.

PROCESS FOR FREEING- PAI'ER PULP FROM IMPURITIES.

Application filed February 16, 1924. Serial No. 693,270.

To all whom it may concern:

Be it known that I, HERMANUS THOMAS- SEN, a subject of the Queen of theNetherlands, residing at Heelsum, the Netherlands, have invented certainnew and useful Improvements in Processes for Freeing Paper Pulp fromImpurities, of which the following is a specification.

In order to free paper pulp or other fibrous material from impuritiessuch as sand or grit before it flows to the paper machine, it isgenerally run through a sand trap or grit retainer which may consist ofa trough in which are arranged one behind the other oblique cross bars.The paper pulp having to flow up over each of these bars and thendescend, the heavier components such as sand are separated out in thetrough. In order to retain as far as possible any knots or improperlydivided portions of paper fibre a strainer is also used in the form of avery fine meshed sieve.

The sand trap is, however, a not altogether satisfactory arrangementbecause it does not keep back all the heavy impurities and the lighterimpurities it allows to pass. Moreover the paper pulp is liable to clogin the sand trap and then to free itself in. comparatively lar e masseswhich block up the strainer. In fins respect the sand trap has hithertoconstituted an unavoidable evil.

The present invention makes the usual sand trap and even the strainerquite unnecessary. The invention consists in a process where y theheavier and the lighter impurities are all removed and then the knottedand tangled fibres are separated out of the pulp without thedisadvantages of the known types of sand trap being experienced. Insteadof these disadvantages the process presents certain essentialadvantages.

According to the invention the paper pulp is not led through a sand trapbut into a rotating drum with unperforated sides. It has been foundpossible by this means to throw out the heavier particles from the paperpulp, without the paper fibres, which themselves possess a higherspecific. gravity than water, being thrown out. It is only necessary torotate the drum at a suitable and not too high speed. The speed ofrotation of the drum can be so selected that the knots are thrown outfrom the paper pulp but not the loose fibres. In this case the straineris made unnecessary and paper can be produced which contains noimpurities. The lighter particles can be retained in the drum by meansof a ring, the distance of which from the side. of the drum is less thanthe thickness of the layer of paper pulp, which in turn is determined bythe width of the inwardly directed upper edge of the drum.

In the accompanying drawing is illustrated an apparatus for carrying outthe invention, Fig. 1 being a sectional elevation and Fig. 2 a planview.

The hollow shaft 1 carries the bottom 2 of the rotating drum the side 3of which is let into the bottom. The drum during operation is rapidlyrotated by means of a pulley 4 and gear wheels 5 and 6. The paper pulpwhich is to be freed from impurities is fed in through the centre tube 7which is provided with a wide flange 8. The vanes 9 cause the paper pulpon the bottom 2 of the drum 10 to rotate rapidly and a cylindrical layerof paper pulp is formed which lies against the side 3 of the drum, thelayer being of a thickness determined by the width of the flange orinturned upper edge 10 of the drum.

In proportion as the paper pulp is fed into the drum through the tube 7,pulp is thrown out of the drum over the edge 10.'

Particles havinga greater specific gravity such as sand, metal particlesand also the fibre knots remain at the side 3 of the drum, whilst thelighter particles are held back by the ring 11, which at its outer edgeis of greater diameter than the ring 10 at its inner edge, so that thecleansed paper pulp is caught in the stationary receiver 12 from whichit is taken to. the paper making machine.

The hollow shaft 1 during operation is closed at its upper end. Thisshaft is made hollow in order to simplify cleaning of the drum 2, 3, forwhich operation the shaft is opened at the top.

The advantages of the new process are the following 1. The lighterimpurities are removed,

2. The paper fibres which easily become felted during preparatorytreatment are completely separated from one another, so

that the paper pulp flows to the paper ma- 3. The loose fibres are lesslikely to 010 the strainer if one is used than the felte fibres whichoccur with the hitherto known processes.

4. The thickness of the paper can be instantaneously adjusted byaltering the admission fiow of the paper pulp into the centrifugalmachine; previously the whole of the contents of the sand trap had to beallowed to flow through the machine.

5. Filling materials such as kaolin, heavy spar or the like can'berapidly and quite uniformly mixed with the paper pulp in the centrifugalmachine.

6. Colouring matters can be added imme- V diately before the papermachine is reached substantially cylindrical layer, collecting theheavier impurities at the outside of the layer, collecting the lighterimpurities at the inner I surface of said layer and discharging thepurified pulp from between the said impurities.

2. In a process for removing impurities and knots or the like from paperpulp and other fibrous material, supplying the pulp continuously to acentrifugal separator, r0- tating the separator at a speed sufiicient tocause the pulp to accumulate in a cylindrical layer and to cause theknots or the like and the heavy impurities to accumulate at the outersurface of the layer, retaining the said knots and impurities in theseparator, I

retaining the lighter'impurities at the internal surface of the layer ofplup, and discharging from between the outer and inner surfaces of thesaid layer purified pulp free from impurities and knots or the like.

3. Apparatus for use in freeing paper pulp or other fibrous materialfrom impurities, comprising a centrifugal separator, a rotary separatordrum, means for supplying the pulp to the center of the drum, vanes inthe drum for rotating the pulp, means in the drum for retaining thereinthe heavier and i also the li hter impurities and means for receivingtIie purified pulp discharged by centrifugal force from between thelighter and the heavier impurities in the drum.

In testimony whereof I afiix my signature.

HERMANUS THOMASSEN.

